Roller clutches, which are often found in automatic transmission applications, generally include a plurality of spring energized rollers, each of which is located between a cylindrical pathway on one race and one of a series of sloped cam ramps on a coaxial cam race. A great advantage of roller clutches is that each roller, given its independent spring energizing, automatically self seeks its own unique and optimal ready position during overrun, that is, the position where it will be lightly engaged between the pathway and its cam ramp, ready to quickly jam between the races when overrun conditions end. As the clutch overruns, each roller moves up and down its cam ramp, generally called roller travel, which can be quite rapid, and must be allowed to occur freely. It is also desirable that the rollers be maintained parallel to the race axis as they travel.
The typical roller clutch includes a fairly rigid cage, which provides its basic structural framework, and which also retains the rollers and mounts the energizing springs. The cage-roller-spring unit can then be installed in one step between the clutch races, with the cage sliding over and locking to the cam race. After installation, the cage remains generally coaxial to the races. Each roller is usually retained by the cage in an individual roller retention pocket defined by a pair of axially spaced side rails of the cage. These side rails may be metal end rings, extensions of a plastic journal block, or any other cage structure that will suitably axially confine the rollers as they travel. Because the clutch cage is maintained substantially coaxial to the races after installation, the side rails of the retention pockets are maintained generally perpendicular to the axis of the races, and provide some measure of guidance to keep the rollers parallel to the race axis as the roller ends slide along the inside surfaces of the side rails. However, the inside surfaces of the retention pocket side rails must have a fair degree of clearance from the roller ends, so as not to interfere with their free travel, and so cannot rigorously guide the rollers. The rollers are thus subject to being skewed away from the race axis, especially at high speeds, or where external roller disturbing forces are present.
The typical roller energizing spring is an accordion type compression spring that is also located within the roller retention pocket, compressed between its respective roller and a spring mounting portion of the cage, which is generally a cage cross bar. Therefore, the working length of the spring is limited to the room available between the roller and the cage cross bar. The spring is not particularly strong or stiff, as it must move back and forth freely with the roller, and would add to race wear if it were too strong. Consequently, the spring generally follows the roller without providing significant roller guidance. Furthermore, the spring is potentially subject to being disturbed or damaged by the roller as it moves. Often, the roller is subject to various external forces during clutch overrun that can skew it off axis or move it so far down the cam ramp that it loses contact with one or both race surfaces, generally referred to as roller pop out. In such cases, the spring is subject to warping and kinking, and may potentially lose contact with the roller altogether, or be over compressed. Such considerations may dictate the use of a more costly sprag clutch in such an environment.